This section provides background information related to the present disclosure which is not necessarily prior art.
1. Technical Field
This invention relates to a substrate support apparatus for a printer, for example including a printer table, for example for use in a flat bed printer. In examples described, the table comprises a vacuum table for holding a substrate in a printer.
2. Discussion
Vacuum tables are well known for use in supporting a substrate in a flat bed printer. In a common type of vacuum table, the table includes an upper surface for supporting a substrate being printed. A plurality of apertures is provided in the surface of the table, the apertures being connected to a source of negative pressure. The substrate is placed onto the table for printing, the substrate covering apertures on the table surface. During printing, when the negative pressure is applied, air is drawn through the apertures in the table; the negative pressure can therefore act to hold the substrate to the table.
However, problems can arise where the size of the substrate is less than the area of the table populated by the apertures. In such a situation, when the substrate is placed on the table, apertures remain uncovered by the substrate. Leaving such apertures uncovered during printing can be disadvantageous because the pressure source needs to be run at a relatively high power for sufficient negative pressure to be applied to hold the substrate to the table compared to an arrangement where all of the apertures are covered. The greater the numbers of apertures remaining uncovered, the greater the problem.
An additional problem can arise where apertures remain uncovered during a printing operation. Open apertures can lead to a high airflow near printhead nozzles, which can disrupt printing and/or lead to a reduction in print quality.
In an attempt to improve this arrangement, a mask is applied to the table to cover the apertures not covered by the substrate. Such masks may comprise for example paper or card or a plastics sheet material cut to the appropriate shape. In particular in cases where the area of the table not covered by the substrate is of particularly irregular shape, the mask may comprise several mask elements.
In some cases, satisfactory results can be obtained where the mask is simply placed on the table, because the application of the negative pressure during printing will also act to hold the mask to the table. However, in practical applications, it is generally desirable to fix the mask to the table, in particular where a similar layout of substrates is to be used for several consecutive printing operations. For example, it is common practice that, once the printing on the substrate is complete, the pressure source provides a positive pressure to the apertures on the table to assist in removal of the printed substrate. Such application of positive pressure has the effect also of dislodging the mask which, in particular where several substrates are to be printed using the same mask arrangement, is disadvantageous.
Where the mask comprises a plastics sheet, a tacky or adhesive backing may be provided to hold the mask to the surface. However, this can leave an adhesive residue on the surface of the table. Also, such a mask is not suitable for repeated application and removal from the table and can have a limited service life.
Alternatively, in particular where the mask comprises paper or card, the mask may be fixed in place on the table, for example using adhesive tape. However, such taping is labour intensive and adds significant time to the print cycle.
A further problem is that the tape used and/or the adhesive is often not resistant to the effects of radiation, for example UV radiation and/or heat to which it can be exposed during the printing cycle. In particular for masks subjected to several printing cycles, this can lead to loss of adhesion between the tape or mask material and the table and lifting and/or curling of the tape or mask material. This can then lead to loss of printing quality and/or halting of the printing cycle to reattach the tape.
If several sets of one or more substrates of similar configuration are to be printed using the same mask arrangement, then the mask is usually retained on the table for the printing of the sets of substrates. This can lead to a greater risk of the tape holding the mask becoming dislodged. Also, as mentioned above, it is common practice for the pressure source to be used to blow air through the apertures after the printing operation to assist in the removal of the substrate. This practice can lead to damage of the mask, and/or greater risk of parts of the tape and/or mask lifting from the table.
Attempts to overcome these problems have led to systems in which the apertures are arranged in zones on the table, the pressure applied to each zone being independently controllable. Thus in such arrangements one or more pressure sources are used selectively to apply negative pressure to one or more of the zones in an attempt to arrange for the negative pressure only to be applied to apertures covered by the substrate. However, experience of these systems has shown that the zones often do not correspond to the shapes of the substrates to be printed, and so some masking is often required even in such systems. Also, the pressure supply mechanism is greatly increased in complexity and cost to support the zones.
Aspects of the invention seek to overcome or mitigate one or more of these or other problems.